Thyroid stimulating hormone

Thyroid-stimulating hormone (TSH) or thyrotropin is a hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3), which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.

Structure

TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit. The alpha subunit is nearly identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG). The beta subunit is distinct for TSH, and therefore determines its receptor specificity.

Function

The primary function of TSH is to stimulate the thyroid gland to produce thyroid hormone. The release of TSH is regulated by a closed-loop system. When levels of T3 and T4 are low, the production of TSH is increased, and conversely, when levels of T3 and T4 are high, the production of TSH is decreased.

Clinical significance

TSH is used as a diagnostic test for various thyroid disorders. A high level of TSH suggests an underactive thyroid, or hypothyroidism, while a low level of TSH suggests an overactive thyroid, or hyperthyroidism.

See also

• Thyroid function tests
• Hypothyroidism
• Hyperthyroidism

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